Dryer area defects

Note: In the drying section, even drying with as high an evaporation rate as possible is the aim.
However, the following defects and their causes do arise, and breaks in this section may result from any of the causes that will give breaks at the press; lumps, light spots, or any straining of the sheet at any point before the dryers.
1. Picking may be due to:
— too high a temperature in first dryer section.
— slime spots.
— a sizing change.
2. Dry cuts or cockles may be caused by:
— improper slice adjustment.
— poor pressing.
— over-dry paper.
— too much crown in top rolls of calender stack.
— press section rolls with insufficient crown to relieve the edge.
3. Pockmarks may be caused by:
— dirty dryers.
— dirty dryer felts.
— excessively wet paper going through the dryers.
— dryers are too hot.
— a dirty top calender roll.
4. Dryer felt marks may be due to:
— protruding rivet heads.
— water in the dryers.
— soft stock.
— an excessively wet sheet going through the dryers.
— an old (filled up) dryer felt.
5. Slugs may be due to:
— drops of water from the ceiling or the dryer hood.
— dirty dryer felts or dryers (particles of dirt prevent the sheet from drying properly).
— the dryers may not be scraped often enough.
6. Calender cuts are due to:
— improper crown on the rolls.
— rolls out of alignment.
— too slack a draw between the dryers and calender.
— wet paper.
— a dragging calender bearing.
— a plugged stack with a flat spot on the roll.
7. Scabs can be caused by:
— pitch spots on the calender stack.
— pieces of paper sticking to the calender stack.
— by a fault in the size press solution.
8. Pinholes can be caused by:
— particles of grit, cement, etc., stuck in the sheet that drop out at the calender stack.
9. Fiber cuts are due to:
— hard spots on the reel (a cut if in the middle of the sheet or a break if at the edge of the sheet).
— shives.
10. Hair cuts are caused by:
— human hair or rope fibers cutting the sheet when going through the calender stack.
— by wool fibers shredding from wet felts.
11. Turnover at the winder or reel is usually due to hard edges.
12. Corrugations (large and narrow) can be caused by soft spots in the reel between hard spots.
— check the spreader bar adjustment.
— check the air on the stack.
— examine the stacks for moisture streaks.
13. Loose paper in the roll is due to:
— a dirty stack.
— a dirty floor around the winder (clean up after each set).
— paper on the floor picked up by static electricity.
— a drafty room around the winders.
— loose paper put in the reel to build it up at the start.
14. Dust in the roll can be caused by:
— improper setting of the slitters.
— dull slitters.
— sanding the rolls when running.
— a dirty floor.
— not cleaning the winders often enough.
— a rough or dirty spreader bar.
15. Defective splices can be caused by:
— applying splicing tape too close to the edge of the joint causing the companion sheet to adhere.
— placing the splicing tape too far back from the joint, causing the bottom edge to turn back.
— irons at improper temperatures; sloppy tear off.
— defective tape; some makes of heat-setting tape have a poor shelf life and deteriorate rapidly if stored at machine room temperatures.
16. Wrinkles at the reel or winder are caused by:
(a) reel:
— wet streaks.
— slack draws.
— an improperly adjusted spreader bar.
— a bad reel (hard spots).
(b) winder:
— an improperly adjusted spreader bar.
— running the reel with wet streaks.
— a poor core.
— poor splices.
— an out-of-round core shaft.
— improper tension control.
17. Winder cracks can be caused by:
— hard edges.
— too tight a wind.
— cracked cores and core tips.
— cores being too slack on the core shaft.
— a rider roll allowed to remain too long on the roll.
— fiber cuts and hairs.
— cores of different sizes.
18. Soft spots and hard spots can be caused by:
— uneven distribution on the forming fabric.
— improper pressing.
— an old second press felt.
— old or dirty dryer felts.
— improper calendering.
— improper focusing of calender air on the affected spots on calenders.